The objective of this proposal is to identify genes that are unique to E. coil O157:H7 (E. coil O157) isolates capable of causing hemolytic uremic syndrome (HUS) in humans, and develop a signature profiling system for such isolates. Toward this objective, a HUS-causing E. coil O157 isolate will be compared to a bovine E. coil O157 isolate from lineage II that is incapable of human infection. Convalescent sera from patients who had HUS will be absorbed with a library made from the genomic DNA of the bovine E. coil O157 isolate, and then used to screen a library made from the genomic DNA of the HUS-causing E. coil O157 isolate. Genes unique to the HUS-causing isolate will be identified and PCR primer pairs derived from their DNA sequences will be used to establish a signature profiling system. All of these signature profiling primer pairs will then be evaluated against a collection of O157 isolates from different sources and disease outcomes. The proposed immunological approach will provide a more direct, powerful and relevant-to-infection approach to the detection of genes unique to the HUS-causing isolates. We anticipate that this research will facilitate the development of a signature profiling system to help prognosticate human disease outcome, aid in the development of specific therapeutic measures, and improve epidemiological surveillance.